The present invention is directed to improved end closures for pasted valve, stepped end bags and more particularly to improved end closures that render such bags substantially sift resistant.
All pasted valve, stepped end bags have three scored folds in each corner. Two of the scores are provided for folding the overlapping flaps that form the top and bottom closures of the bag. The third score is created by the edge folds at each side of the bag when the tubular bag structure is formed. These scores ultimately become the center scores in each infolded flap at each corner of the bag. Pasted valve, stepped end bags are highly prone to sifting through the channels formed by these scores. In addition, such bags are also prone to leakage in and around the valve area when a valve sleeve is improperly located or not completely closed.
Paper bags of the pasted valve, stepped end type (PVSE) are in common use for packaging bulk materials. Such bags are made from tough, strong paper or other fibrous material, and usually have walls comprising multi-ply layers to increase their strength. The bags are used for packaging many kinds of bulk materials such as cement, fertilizer, feed grain, flour and the like and are filled by inserting a filling nozzle through the valve (or valve sleeve where provided), and blowing the material therein. After filling, the nozzle is withdrawn and the valve is automatically closed by the weight of the material in the bag when the bag is turned upside down, or where valve sleeves are provided, the valve sleeve may be closed with a fold and tuck, or with a hot melt adhesive or the like.
Valve sleeves are usually made from a single sheet of paper or other material to form a tube and the tubular sleeve is adhesively secured to the valve flaps. In a PVSE bag, the sleeve is adhesively secured between the overlapping pasted outer flaps and one of the infolded panels at a corner of the bag. Various attempts have been made in the past to make such bags and valves leak resistant and to overcome the sifting problems occuring at both ends, however, none of the prior attempts have achieved the success of the present invention.